Inorganic nanowires

ABSTRACT

An inorganic nanowire having an organic scaffold substantially removed from the inorganic nanowire, the inorganic nanowire consisting essentially of fused inorganic nanoparticles substantially free of the organic scaffold, and methods of making same. For example, a virus-based scaffold for the synthesis of single crystal ZnS, CdS and free-standing L10 CoPt and FePt nanowires can be used, with the means of modifying substrate specificity through standard biological methods. Peptides can be selected through an evolutionary screening process that exhibit control of composition, size, and phase during nanoparticle nucleation have been expressed on the highly ordered filamentous capsid of the M13 bacteriophage. The incorporation of specific, nucleating peptides into the generic scaffold of the M13 coat structure can provide a viable template for the directed synthesis of a variety of materials including semiconducting and magnetic materials. Removal of the viral template via annealing can promote oriented aggregation-based crystal growth, forming individual crystalline nanowires. The unique ability to interchange substrate specific peptides into the linear self-assembled filamentous construct of the M13 virus introduces a material tenability not seen in previous synthetic routes. Therefore, this system provides a genetic tool kit for growing and organizing nanowires from various materials including semiconducting and magnetic materials.

This application is a Continuation of U.S. application Ser. No.10/976,179, filed Oct. 29, 2004, which claims benefit under 37 U.S.C.§119(e) to U.S. Provisional Application No. 60/534,102, filed Jan. 5,2004, which are hereby incorporated by reference in their entirety.

This invention was made with government supported awarded by the ArmyResearch Office under Grant Number DAAD19-03-1-0088. The government hascertain rights in the invention.

INTRODUCTION

The reliance of a wide variety of technologies on developing scalableand economic methods for the fabrication of one-dimensional materials,including nanowires and nanotubes, has spurred intense and rapidprogress in the area of materials synthesis. For example,one-dimensional materials have been enthusiastically pursued for theirapplications in the study of, for example, electrical transport (1),optical phenomena (2), and as functional units in nanocircuitry (3).Pursuit of “bottom up” methods for the synthesis of semiconducting,metallic and magnetic nanowires has yielded a variety of syntheticstrategies including, but not limited to, Vapor Liquid Solid (VLS) (4),chemical (5), solvothermal, vapor phase, and template-directedfabrication (6). Although each method developed for the production ofnanowires has had some basic success in achieving high qualitymaterials, methods to date have not yielded monodisperse, crystallinenanowires of radically different compositions. In general, prior methodsfor nanowire production can be erratic, synthetically cumbersome, andare not universal. See, for example, U.S. Pat. No. 6,225,198 toAlivisatos et al. for II-VI semiconductor production in liquid media andreferences cited herein. Reference 4 to Lieber et al. describes thedifficulty in finding a universal approach. It describes a VLS processthat requires use of lasers and high temperatures and produces ananowire having a nanoparticle at the end which may not be desirable.

Recently, biological factors have been exploited as synthesis directorsfor nanofibers (7, 8), virus-based particle cages (9), virus-particleassemblies (10, 11, 12), and non-specific peptide templates (13). Thisis due to the high degree of organization, ease of chemical modificationand naturally occurring self-assembly motifs in these systems.

Belcher et al. have prepared nanowires associated with and bound togenetically engineered viral scaffolds (see, for example, U.S. PatentPublication, 2003/0068900 to Belcher et al.). The scaffolds serve as atemplate as nanoparticles or nanocrystals form on the scaffold. Althoughthis technology is attractive and provides important advantages, a needexists to improve upon it. For example, it is desirable to generateimproved properties such as improved fusion between the nanocrystals andreduction in defects. It is also desirable to fuse the nanocrystals intoone long single crystal rod or into large crystalline domains. Moreover,it is desirable in many applications to not have and substantiallyeliminate the viral scaffold bound to or associated with the viralscaffold. Moreover, it is desirable to control the size and sizestatistical distributions for the nanowires including, for example,prepare monodisperse materials and materials having controlled length.If possible, the nanowires should be usable directly, without need for asize-based separation step before use. A need also exists to be able toconnect the nanowires with other components such as electrodes whichallow the nanowires to be commercially useful. These connections should,if possible, not be mere chance connections but be strategicallydirected and controllable.

References numerically cited in this specification are provided in alisting at the end of the specification and are incorporated byreference in the specification in their entirety.

SUMMARY

The present invention in many of its embodiments is summarized in thisnon-limiting summary section.

In one embodiment, the present invention provides an inorganic nanowirehaving an organic scaffold substantially removed from the inorganicnanowire, the inorganic nanowire consisting essentially of fusedinorganic nanoparticles substantially free of the organic scaffold (“theinorganic nanowire of embodiment 1”).

The present invention also provides compositions and devices comprisinga plurality of these inorganic nanowires. In another embodiment, thepresent invention provides a composition comprising a plurality ofinorganic nanowires, wherein the inorganic nanowires comprise fusedinorganic nanoparticles substantially free of organic scaffold.

In another embodiment, the present invention provides a method offorming an inorganic nanowire comprising the steps of: (1) providing oneor more precursor materials for the inorganic nanowire; (2) providing anelongated organic scaffold; (3) reacting the one or more precursormaterials in the presence of the scaffold to form nanoparticles, whereinthe nanoparticles are disposed along the length of the elongated organicscaffold; and (4) thermally treating the scaffold and the nanoparticlesto form the inorganic nanowire by fusion of the nanoparticles. In someembodiments, the organic scaffold can be removed, such as during thethermal treatment. The present invention also provides nanowiresprepared by this method.

Also provided is a method of forming an inorganic nanowire comprisingthe steps of: (1) providing one or more precursor materials for theinorganic nanowire; (2) providing an organic scaffold; (3) reacting theone or more precursor materials in the presence of the scaffold underconditions to form the inorganic nanowire. In some embodiments, theorganic scaffold can be removed, such as during the reacting. Thepresent invention also provides nanowires prepared by this method.

The present invention also provides for use of a filamentous organicscaffold as a sacrificial organic scaffold in the production of aninorganic nanowire comprising providing a filamentous organic scaffoldand an inorganic nanowire precursor on the scaffold, converting theinorganic nanowire precursor to the inorganic nanowire while removingthe filamentous organic scaffold to yield the inorganic nanowire.

An additional use provided herein is the use of an elongated organicscaffold to control the length of an inorganic nanowire disposedthereon, comprising the step of genetically engineering the scaffold tocontrol the length of the scaffold.

An important embodiment is also a device comprising an electrode inelectrical contact with the inorganic nanowire of embodiment 1 or anyother nanowire described herein. In another embodiment, the device canfurther comprise at least two electrodes each in electrical contact withthe inorganic nanowire of embodiment 1 or any other nanowire describedherein. Examples of devices include a field effect transistor or asensor. In other embodiments, the device comprises at least twonanowires according to embodiment 1, or any other nanowires describedherein, wherein the nanowires are in a parallel arrangement, or in acrossed arrangement.

The invention also provides a segmented nanowire comprising a pluralityof connected segments of inorganic nanowires of embodiment 1 or anyother nanowires described herein. In some embodiments, the scaffold wasused to form the nanowire and/or direct the placement of the nanowirebefore being removed.

The invention also provides a composition comprising a plurality ofinorganic nanowires, wherein the inorganic nanowires comprise fusedinorganic nanoparticles that were disposed on an organic scaffold. Insome embodiments, the scaffold(s) were used to form the nanowires and/ordirect the placement of the nanowires, such as placement in a circuitsubstrate, before being removed.

The invention also provides a process for producing nanowires with useof an elongated organic scaffold comprising the steps of: (1) providingan elongated organic scaffold which comprises a plurality of bindingsites including binding sites along the length of the scaffold andbinding sites on at least one end of the scaffold; (2) disposing ananowire precursor composition along the length of the scaffold to forma scaffolded precursor composition; and (3) treating the scaffoldedprecursor composition to form the nanowire. In some embodiments, thescaffold is substantially removed, such as during the treating step. Inone embodiment, the elongated organic scaffold has binding sites at bothends of the scaffold. In another embodiment, the process furthercomprises the step of using the binding site at the end of the scaffoldto bind to another structure. For example, the another structure can beanother elongated organic scaffold.

The invention also provides compositions. For example, in oneembodiment, a nanowire composition is provided comprising a nanowirewith a thermodynamically high energy phase, or a collection of nanowiresaccording to this embodiment, wherein the nanowires are substantiallymonodisperse in length, width, or length and width. In this embodiment,the nanowire can be an inorganic nanowire such as, for example, ananowire of semiconductive material, metallic material, metal oxidematerial, magnetic material, or mixtures thereof.

The invention also provides an inorganic nanowire comprising fusedinorganic nanoparticles, or a composition comprising a collection ofinorganic nanowires according to this embodiment. In this embodiment,the invention also provides an inorganic nanowire comprising fusedinorganic nanoparticles comprising semiconductor material, metallicmaterial, metal oxide material, or magnetic material, as well ascollections of these nanowires.

The invention also provides an inorganic nanowire consisting essentiallyof fused inorganic nanoparticles that were disposed on an organicscaffold.

A basic and novel feature for many embodiments of the present inventionis the substantial elimination of the organic scaffold when it is usedto prepare the nanowire. In many embodiments, its preferred that theorganic scaffold be totally eliminated. Moreover, a basic and noveladvantage in many embodiments is that the nanowires can be fabricateddirectly with good monodispersity without use of a size-based separationof some nanowires from other nanowires.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-D illustrate viruses which can be used as scaffolds.

FIGS. 2A-F provide characterization of nanowires made of semiconductormaterial.

FIGS. 3A-F provide characterization of nanowires made of magneticmaterial.

DETAILED DESCRIPTION

I. Introduction

The present invention provides, in one embodiment, an inorganic nanowirehaving an organic scaffold substantially removed from the inorganicnanowire, the inorganic nanowire consisting essentially of fusedinorganic nanoparticles substantially free of the organic scaffold. Thepresent invention also provides compositions comprising a plurality ofthese inorganic nanowires. This invention also provides compositionscomprising a plurality of inorganic nanowires, wherein the inorganicnanowires comprise fused inorganic nanoparticles substantially free oforganic scaffold.

The organic scaffold is generally removed so that, preferably, it cannotbe detected on the nanowire. This substantial removal can be describedin terms of weight percentage remaining. For example, the amount ofremaining organic scaffold with respect to the total amount of nanowireand scaffold can be less than 1 wt. %, more preferably, less than 0.5wt. %, and more preferably, less than 0.1 wt. %. A basic and novelfeature of the invention is the substantial removal of the scaffold inthe production of high quality nanowires.

In another patent application, which is hereby incorporated by referencein its entirety, [U.S. Ser. No. 10/665,721 filed Sep. 22, 2003 toBelcher et al. (“Peptide Mediated Synthesis of Metallic and MagneticMaterials”)], additional description is provided for burning off andelimination of a viral scaffold from materials to which the scaffold canselectively bind. In this application, annealing temperatures of500-1,000° C. are described for burning off the scaffold. In addition,Mao et al., Virus-based toolkit for the directed synthesis of magneticand semiconducting nanowires, Science 303:213-217 (2004), which ishereby incorporated by reference including all figures and theexperimental section, includes some teachings that may be useful inpracticing the present invention. Fairley, Peter, (2003) Germs ThatBuild Circuits, IEEE Spectrum 37-41, which is hereby incorporated byreference in its entirety including all figures and use of electrodesconnected by nanowires, also includes teachings that may be useful inpracticing the present invention, such as applications of nanowires.Priority provisional application No. 60/534,102 filed Jan. 5, 2004 byBelcher et al., is hereby incorporated by reference in its entirety.

The detailed description of the invention is organized according to thefollowing sections: (1) introduction, (2) scaffold which issubstantially removed, (3) nanowires, (4) methods of making nanowires,(5) applications for the nanowires, and (6) working examples.

II. Scaffold

Although the scaffold ultimately may be substantially removed from thenanowire, the scaffold is an important part of the invention. In thepractice of the present invention, one skilled in the art can refer totechnical literature for guidance on how to design and synthesize thescaffold including the literature cited herein and listed at theconclusion of the specification. For example, although the presentinvention relates to organic scaffolds and is not limited only to viralscaffolds in its broadest scope, viral scaffolds are a preferredembodiment. In particular, an elongated organic scaffold can be usedwhich is a virus, and the term virus can include both a full virus and avirus subunit such as a capsid. The literature describes the preparationof viral scaffolds through genetic engineering with recognitionproperties for exploitation in materials synthesis. This includes use ofviruses in the production of inorganic materials which havetechnologically useful properties and nanoscopic dimensions. In thepresent invention, one skilled in the art can use the literature in thepractice of the present invention to prepare inorganic nanowires onscaffolds, wherein the scaffolds are later substantially eliminated sothat the inorganic nanowire is substantially free of the scaffold. Whenthe scaffold is intended to be removed, the scaffold may be referred toas a “sacrificial scaffold.”

One skilled in the art, for example, can refer to the following patentliterature for selection of the virus, genetic engineering methods, andfor materials to be used with genetically engineered viruses. Phagedisplay libraries and experimental methods for using them in biopanningare further described, for example, in the following U.S. patentpublications to Belcher et al.: (1) “Biological Control of NanoparticleNucleation, Shape, and Crystal Phase”; 2003/0068900 published Apr. 10,2003; (2) “Nanoscale Ordering of Hybrid Materials Using GeneticallyEngineered Mesoscale Virus”; 2003/0073104 published Apr. 17, 2003; (3)“Biological Control of Nanoparticles”; 2003/0113714 published Jun. 19,2003; and (4) “Molecular Recognition of Materials”; 2003/0148380published Aug. 7, 2003, which are each hereby incorporated by referencein their entirety. Additional patent applications useful for one skilledin the art describe viral and peptide recognition studies with use ofgenetically engineered viruses for materials synthesis and applicationsincluding, for example, (1) U.S. Ser. No. 10/654,623 filed Sep. 4, 2003to Belcher et al. (“Compositions, Methods, and Use of Bi-FunctionalBioMaterials”), (2) U.S. Ser. No. 10/665,721 filed Sep. 22, 2003 toBelcher et al. (“Peptide Mediated Synthesis of Metallic and MagneticMaterials”), and (3) U.S. Ser. No. 10/668,600 filed Sep. 24, 2003 toBelcher et al. (“Fabricated BioFilm Storage Device”), (4) U.S.provisional Ser. No. 60/510,862 filed Oct. 15, 2003 and the U.S. utilityapplication Ser. No, 10/965,665 filed Oct. 15, 2004 to Belcher et al.(“Viral Fibers”); and (5) U.S. provisional Ser. No. 60/511,102 filedOct. 15, 2003 and the U.S. utility application Ser. No. 10/965,227 filedOct. 15, 2004 to Belcher et al. (Multifunctional Biomaterials . . . ”);each of which are hereby incorporated by reference. These referencesdescribe a variety of specific binding modifications which can becarried out for binding to conjugate structures, as well as forming theconjugate structures in the presence of the material modified forspecific binding. In particular, polypeptide and amino acid oligomericsequences can be expressed on the surfaces of viral particles, includingboth at the ends and along the length of the elongated virus particlesuch as M13 bacteriophage, including pIII and pVIII expressions, as wellas pIX, pVII, and pVI expressions, and combinations thereof. Using theseexpression sights, the viruses may be engineered to express surfacepeptides along the length of the virus, at the ends of the virus, or anynumber of other sites and combinations of sites. A single site formodification can be modified with more than one unit for specificbinding. For example, a pVIII site can be modified to have twodistinctly different binding units. In addition, different sites formodification can be modified with the same or different units forbinding. For example, the ends of the virus particles can be modified tobind to specifically bind a first material, while the body of the virusparticles can be modified to bind a second material. Multiple bindingsites can be used to create multifunctional scaffolds that can be usedto form nanowires with specifically engineered and varying compositionsamong other applications. The binding sites can be designed so thatnanoparticles nucleate at the binding sites or the binding sites can bedesigned to bind preformed nanoparticles. The scaffold can befunctionalized with sufficient binding units to achieve the desiredconcentration needed to form the nanowire.

In addition, the paper “Selection of Peptides with Semiconductor BindingSpecificity for Directed Nanocrystal Assembly”; Whaley et al., Nature,Vol. 405, Jun. 8, 2000, pages 665-668, herein incorporated by reference,describes a method of selecting peptides with binding specificity usinga combinatorial library. Specifically, the article shows a method ofselecting peptides with binding specificity to semiconductor materialsusing a combinatorial library with about 10⁹ different peptides. Thecombinatorial library of random peptides, each containing 12 aminoacids, were fused to the pIII coat protein of M13 coliphage and exposedto crystalline semiconductor structures. Peptides that bound to thesemiconductor materials were eluted, amplified, and re-exposed to thesemiconductor materials under more stringent conditions. After the fifthround of selection, the semiconductor specific phages were isolated andsequenced to determine the binding peptide. In this manner, peptideswere selected with high binding specificity depending on thecrystallographic structure and composition of the semiconductormaterial. The technique can be modified to obtain peptides with abinding specificity for not just semiconductor materials, but a range ofboth organic and inorganic materials.

One skilled in the art can also refer to, for example, C. E. Flynn etal. Acta Materialia, vol 13, 2413-2421 (2003) entitled “Viruses asvehicles for growth, organization, and assembly of materials.” Thisreference, as well as all references cited therein, are incorporatedherein by reference in their entirety. In addition, reference 12 below(Mao et al., PNAS) is hereby incorporated by reference for all of itsteachings including the nucleation and structures shown in FIG. 1. Also,in particular, reference 17 (Flynn et al., J. Mater. Chem) is alsoincorporated by reference in its entirety including descriptions ofusing aqueous salt compositions to nucleate nanocrystals which aredirected in their crystal structure and orientation by the recognitionsites. In the present invention, these nucleated nanocrystals can beconverted to single crystalline and polycrystalline nanowires, whereinthe scaffold is substantially removed.

The scaffold is further described including the role of geneticprogramming for the preferred embodiments. Although the viral scaffoldsrepresent a preferred embodiment, the present invention comprises othertypes of non-viral scaffolds as well. Also, although M13 virus is apreferred embodiment for a scaffold, the present invention is notlimited to this virus.

The scaffold can comprise an entire virus, a virion, or viral subunitsincluding capsids. Viral subunits including proteins, peptides, nucleicacids, DNA, RNA, and the like, in various combinations. The scaffolddoes not require that both peptide and nucleic acid be present. Forexample, virus mimics can be used or engineered, wherein the size,shape, or structure mimics that of a virus, but the does not containnucleic acid and/or may not have the ability to infect a host forreplication. One skilled in the art can prepare viral scaffolds based onpurely synthetic methods from the bottom up as well as using moretraditional methods wherein materials are supplied by nature without orwithout modification by man.

In a preferred embodiment, wherein the scaffold is a virus or a virussubunit, the scaffold is tailored and designed in structure and functionby genetic programming and/or genetic engineering for production of theone dimensional materials such as nanowires. The genetic programming canbe used to tailor the scaffold for the particular application, andapplications are described further below. The references in Section Idescribe genetic programming which is further described in this sectionfor use in practice of the present invention. See, e.g., GeneticallyEngineered Viruses, Christopher Ring and E. D. Blair (Eds.), BiosScientific, 2001, for descriptions of developments and applications inuse of viruses as vehicles and expressors of genetic material including,for example, prokaryotic viruses, insect viruses, plant viruses, animalDNA viruses, and animal RNA viruses. In the present invention, geneticprogramming can be carried out to engineer a scaffold using thedifferent displayed peptide features of a virus such as, for example, afilamentous bacteriophage such as, for example, the M13 virus which hasa rod shape. Genetic programming can be used to control the scaffold formaterials synthesis, the viral scaffold comprising one or more viralparticle subunits which may or may not include the nucleic acid subunitof the virus. Also, the scaffold may or may not retain infectability.

An overall commercial advantage to this genetic programming approach tomaterials engineering, in addition to materials-specific addressability,is the potential to specify viral length and geometry. For example, anelongated organic scaffold may be genetically engineered to control thelength of the scaffold. This engineering of length can allow the designof nanowires of specific, controlled lengths, for example. Hence, avariety of methods can be used to control the scaffold length andgeometry.

For example, the length of a filamentous virus is generally related tothe size of its packaged genetic information and the electrostaticbalance between the pVIII-derived core of the virion and the DNA. See,e.g., B. K. Kay, J. Winter, J. McCafferty, Phage Display of Peptides andProteins: A Laboratory Manual, Academic Press, San Diego, 1996;Greenwood et al., Journal of Molecular Biology 217:223-227 (1992). Phageobserved by AFM generally are seen to be roughly 860 nm and as short as560 nm depending on whether the complete M13 genome or smaller phagemidare used in sample preparation. See, e.g., reference 12, C. Mao, C. E.Flynn, A. Hayhurst, R. Sweeney, J. Qi, J. Williams, G. Georgiou, B.Iverson, A. M. Belcher, Proc. Natl. Acad. Sci. 2003, 100, 6946. Also,changing a single lysine to glutamine on the inner-end of pVIII canresult in particles approximately 35% longer than wild type phage. See,e.g., J. Greenwood, G. J. Hunter, R. N. Perham, J. Mol. Biol. 1991, 217,223.

In addition, specific linkage, binding, and concatenation of virusparticles can help produce longer viral scaffolds, and thus longernanowires. The multiplicity of additions can be controlled byengineering binding motifs into one virus, which then can accuratelyrecognize binding sites on another virus. For example, the pIII proteinresides at one end of the M13 virus and can be exploited to displaypeptide and protein fusions. At the other end of the virus, the pIX andpVII proteins also can be subject to modification. For example, Gao andcoworkers utilized pIX and pVII fusions to display antibody heavy- andlight-chain variable regions. [See, e.g., C. Gao, S. Mao, G. Kaufmann,P. Wirsching, R. A. Lerner, K. D. Janda, Proc. Natl. Acad. Sci. 2002,99, 12612] See, also, for example, U.S. Pat. No. 6,472,147 for geneticmodification of viruses. These end modifications may be used to link thevirus particles directly or the end modifications may specifically bindto a linker. The linker may be any suitable material. For example, thelinker can be a nanoparticle, amino acid oligomer, nucleic acidoligomer, or a polymer. This present invention encompasses dual-endviral display, either for generating bimodal heterostructures, or incombination with pVIII, producing end-functionalized nanowires.

In addition, dual-end directional linkages enable creation of otherinteresting and commercially useful geometries, such as rings, squaresand other arrays. The binding of one end of a virus directly to theother end of the virus without the use of a linker can be used to formrings, wires, or other viral based structures as well. By engineeringrecognition sites and the corresponding conjugate moieties into a singlevirus, or multiple viruses, the entire system can be geneticallyprogrammed.

An important advantage of the invention is that the organic scaffold canbe an active scaffold, wherein the scaffold not only serves as atemplate for synthesis of the inorganic nanowire, but also activelyassists in coupling the inorganic nanowire to other structures. Forexample, an organic scaffold which is designed at one end to bind toanother structure can be used to couple the inorganic nanowire to thestructure. The scaffolds and the nanowires can be coupled to each other,for example, to form segments of similar or dissimilar materials. Inthis embodiment, the composition of the nanowire would vary as afunction of length.

Additional description is provided for the types of viral structureswhich can be designed by genetic programming for particular applicationsbased on length control, geometry control, binding control, and thelike. The virus scaffold is not particularly limited, and combinationsof viruses can be used of different types. In general, viruses can beused which can be multifunctionalized. In general, virus particles whichare long, filamentous structures can be used. See, e.g., GeneticallyEngineered Viruses, Christopher Ring (Ed.), Bios Scientific, 2001, pages11-21. Additionally, other viral geometries such as dodecahedral andicosahedral can be multifunctionalized and used to create compositematerials. Virus particles which can function as flexible rods, formingliquid crystalline and otherwise aligned structures, can be used.

In particular, phage display libraries, directed evolution, andbiopanning are an important part of genetic programming of viruses, andviruses can be used which have been subjected to biopanning in the viraldesign so that the virus particles specifically can recognize and bindto materials which were the object of the biopanning. The materials canalso be nucleated and synthesized in particulate form, includingnanoparticulate form, in the presence of the specific recognition andbinding sites. Use of filamentous virus in so called directed evolutionor biopanning is further described in the patent literature including,for example, U.S. Pat. Nos. 5,223,409 and 5,571,698 to Ladner et al.(“Directed Evolution of Novel Binding Proteins”). Additional referenceson the recognition properties of viruses include U.S. Pat. No. 5,403,484(phage display libraries, now commercially available) and WO 03/078451.

Mixtures of two or more different kinds of viruses can be used. Mixturesof virus particles with non-virus materials can be used in formingmaterials which use the present invention.

Virus and virus particle can include both an entire virus and portionsof a virus including at least the virus capsid. The term virus can referto both viruses and phages. Entire viruses can include a nucleic acidgenome, a capsid, and may optionally include an envelope. Viruses asdescribed in the present invention may further include both native andheterologous amino acid oligomers, such as cell adhesion factors. Thenucleic acid genome may be either a native genome or an engineeredgenome. A virus particle further includes portions of viruses comprisingat least the capsid.

In general, a virus particle has a native structure, wherein the peptideand nucleic acid portions of the virus are arranged in particulargeometries, which are sought to be preserved when it is incorporated insolid state, self supporting forms such as films and fibers.

Viruses are preferred which have expressed peptides, including peptideoligomers and amino acid oligomer as specific binding sites. Amino acidoligomers can include any sequence of amino acids whether native to avirus or heterologous. Amino acid oligomers may be any length and mayinclude non-amino acid components. Oligomers having about 5 to about100, and more particularly, about 5 to about 30 amino acid units asspecific binding site can be used. Non-amino acid components include,but are not limited to sugars, lipids, or inorganic molecules.

The size and dimensions of the virus particle can be such that theparticle is anisotropic and elongated. Generally, the viruses may becharacterized by an aspect ratio of at least 25, at least 50, at least75, at least 100, or even at least 250 or 500 (length to width, e.g,25:1).

A wide variety of viruses may be used to practice the present invention.The compositions and materials of the invention may comprise a pluralityof viruses of a single type or a plurality of different types ofviruses. Preferably, the virus particles comprising the presentinvention are helical viruses. Examples of helical viruses include, butare not limited to, tobacco mosaic virus (TMV), phage pf1, phage fd1,CTX phage, and phage M13. These viruses are generally rod-shaped and maybe rigid or flexible. One of skill in the art may select virusesdepending on the intended use and properties of the virus.

Preferably, the viruses of the present invention have been engineered toexpress one or more peptide sequences including amino acid oligomers onthe surface of the viruses. The amino acid oligomers may be native tothe virus or heterologous sequences derived from other organisms orengineered to meet specific needs.

A number of references teach the engineering of viruses to express aminoacid oligomers and may be used to assist in practicing the presentinvention. For example, U.S. Pat. No. 5,403,484 by Ladner et aldiscloses the selection and expression of heterologous binding domainson the surface of viruses. U.S. Pat. No. 5,766,905 by Studier et aldiscloses a display vector comprising DNA encoding at least a portion ofcapsid protein followed by a cloning site for insertion of a foreign DNAsequence. The compositions described are useful in producing a virusdisplaying a protein or peptide of interest. U.S. Pat. No. 5,885,808 bySpooner et al discloses an adenovirus and method of modifying anadenovirus with a modified cell-binding moiety. U.S. Pat. No. 6,261,554by Valerio et al shows an engineered gene delivery vehicle comprising agene of interest and a viral capsid or envelope carrying a member of aspecific binding pair. U.S. Published Patent Application 2001/0019820 byLi shows viruses engineered to express ligands on their surfaces for thedetection of molecules, such as polypeptides, cells, receptors, andchannel proteins.

The genetically engineered viruses can be prepared by methods andvectors as described in Kay, B. K.; Winter, J.; McCafferty, J. PhageDisplay of Peptides and Proteins: A Laboratory Manual; Academic Press:San Diego, 1996, and in particular, chapter 3, “Vectors for PhageDisplay” and references cited therein. In addition, the geneticallyengineered viruses can be prepared by methods as described in, PhageDisplay, A Laboratory Manual, by Barbas et al. (2001) including Chapter2, “Phage Display Vectors” and references cited therein. The type ofvector is not particularly limited. Table 2.1 of Barbas providesexemplary vectors which can be used in various combinations to providethe multifunctional viruses. For example, type 3, type 8+8, and phagemidtype p7/p9 can be combined. Or type 8 and type 3 can be combined alongwith phagemid p7/p9 as desired. One skilled in the art can develop othercombinations based on particular applications. Methods can be developedto either display the peptide on some or substantially all copies of thecoat protein.

M13 systems are a preferred example of a filamentous virus scaffold, butother types of filamentous virus scaffolds can be used as well. The wildtype filamentous M13 virus is approximately 6.5 nm in diameter and 880nm in length. The length of the cylinder reflects the length of thepackaged single stranded DNA genome size. At one end of M13 virus, thereare approximately five molecules each of protein VII (pVII) and proteinIX (pIX). The other end has about five molecules each of protein III(pIII) and protein VI (pVI), totaling 10-16 nm in length. The wild typeM13 virus coat is composed of roughly 2800 copies of the major coatprotein VIII (pVIII) stacked in units of 5 in a helical array.

In sum, evolution of substrate specific peptides through phage displaytechnologies for the directed nucleation of materials on the nanometerscale has been previously reported by papers and patents from AngelaBelcher and coworkers (see above description) and serves as the basisfor the material specificity in the virus scaffold or template (16) ofthe present invention. Screening phage libraries for the ability tonucleate and assemble inorganic systems including, for example, the ZnS,CdS (12, 17), FePt and CoPt systems (18) using commercially availablebacteriophage libraries expressing either a disulphide constrainedheptapeptide or a linear dodecapeptide, has yielded the consensussequences CNNPMHQNC (termed A7; ZnS), SLTPLTTSHLRS (termed J140; CdS),HNKHLPSTQPLA (termed FP12; FePt), and ACNAGDHANC (termed CP7; CoPt).Incorporation of these peptides into the highly ordered, self assembledcapsid of the M13 bacteriophage virus provides a linear template whichcan simultaneously control particle phase and composition, whilemaintaining an ease of material adaptability through genetic tuning ofthe basic protein building blocks. Because the protein sequencesresponsible for the materials growth are gene linked and containedwithin the capsid of the virus, exact genetic copies of this scaffoldare relatively easily reproduced by infection into a large suspension ofbacterial hosts.

To prepare nanowires, an anisotropic scaffold can be used which has theability to collect nanoparticles being formed around it and locate themon the scaffold for fusion into a nanowire. In this invention, aninorganic nanowire composition can be formed having a scaffoldsubstantially removed from the inorganic nanowire. Non-viral scaffoldscan also be used including, for example, a variety of other organicscaffolds including, for example, scaffolds which have peptide orprotein recognition units as side groups on an organic backbone. Forexample, the organic backbone can be a synthetic polymer backbone, whichare well known in the art. For example, polymer scaffolds can be usedincluding for example modified polystyrenes of uniform molecular weightdistribution which are functionalized with peptide units. Anotherexample is branched polypeptides or nucleic acids which are modified tohave recognition sites. Another example is a nanolithographicallyprinted peptide structures such as a line with nanoscale width. Ingeneral, DNA, proteins, and polypeptides can be modified withrecognition units, including peptide recognition units, to function asthe organic scaffold. Suitable recognition units include, but are notlimited to, amino acid oligomers, nucleic acid oligomers, polymers,organic molecules (e.g., antibodies, antigens, cell adhesion factors,and trophic factors), and inorganic materials.

In one embodiment, scaffolds and virus particles can be used which arenot directly genetically engineered. However, in general, desirableproperties can be achieved when the virus is genetically engineered orgenetic engineering is used in designing the scaffold.

III. Nanowires

Using methods described in the previous sections, viruses can begenetically engineered so that they function as a scaffold and bind toconjugate moieties in an overall process which ultimately yields aproduction of inorganic nanowires according to the present invention.For example, a rod-shaped virus can direct the synthesis ofnanoparticulates materials along the length of the rod, and thesenanoparticulates materials can be fused into nanowires.

In the present invention, the conjugate materials can be inorganicmaterials which form nanoparticles including inorganic nanocrystals.From these inorganic nanoparticles, inorganic nanowires can be formedconsisting essentially of the fused inorganic nanoparticles uponsubstantial removal of the scaffold. The conjugate materials and theinorganic nanowires can consist essentially of technologically usefulmaterials such as, for example, semiconducting materials, whether dopedor undoped; metallic materials; metal oxide materials, and magneticmaterials. Various oxide materials including silica and alumina fallwithin the scope of the invention. Additional materials of interest fornanotechnology commercial applications are further described in, forexample: (a) Understanding Nanotechnology, Warner Books, 2002, includingmaterials for circuits such as nanowires and nanotubes described in thechapter “The Incredible Shrinking Circuit”, pgs. 92-103 by C. Lieber.(b) Made to Measure, New Materials for the 21st Century, Philip Ball,Princeton University, (c) Introduction to Nanotechnology, C. P. PooleJr., F. J. Owens, Wiley, 2003. Preferably, for nanowires, the materialsprepared on the scaffold conduct electricity as an electrical conductor,are semiconductive (whether inherently or via doping), transmit light,are magnetic, or possess some other technologically useful property.Other properties include ferroelectric, piezoelectric,converse-piezoelectric, and thermoelectric).

Semiconductors are a particularly important type of inorganic nanowirematerial. The semiconductor material can be, for example, any of thestandard types including alloys thereof including IV-IV Group (e.g., Si,Ge, Si_((1-x))Ge_(x)), III-V Group binary (e.g., GaN, GaP), III-V Groupternary (e.g., Ga(As_(1-x)P_(x))), II-VI Group binary (e.g., ZnS, ZnSe,CdS, CdSe, CdTe), IV-VI Group binary (e.g., PbSe), transition metaloxides (e.g., BiTiO₃), and combinations thereof.

Magnetic materials can be those known in the art includingnanostructured magnetic materials. See, for example, Introduction toNanotechnology, C. P. Poole Jr., F. J. Owens, Wiley, 2003, Chapter 7,pages 165-193 (“Nanostructured Ferromagnetism) and references citedtherein (see, e.g., page 193).

In general, although the present invention is not limited by theory, andthe mechanism of nanowire formation is not fully understood, thenanowires can be structures wherein the nanoparticles form intonanowires and collapse into a fused structure at the end of the process.The porosity of the nanowire is not particularly limited, but ingeneral, non-porous nanowire materials are preferred, particularly forconductive applications wherein porosity could interfere with desiredconductivity.

The nanowire can be crystalline. The nanowire can be a singlecrystalline domain or can have one or more crystalline domains. In oneembodiment, the fused nanoparticles are single crystalline. Thecrystalline phase can be either the thermodynamically favorablecrystalline state or a crystalline state which is not thermodynamicallyfavorable but is locked in by the relative orientation of thecrystalline nanoparticles before fusion. The nanoparticles can beoriented in any manner. For example, the crystallographic axis of thenanoparticles can be oriented with respect to the surface of thescaffold. One can vary the thermal treatment in the method of making(see below) to achieve a desired crystalline structure, or to covertpolycrystalline structures to single crystalline structures. One canalso vary the thermal treatment to remove the organic scaffold. In somecases fusion and organic scaffold removal are achieved at the sametemperature, in other cases, fusion can occur before removal.

The length of the nanowire can be, for example, about 250 nm to about 5microns, or more particularly, about 400 nm to about 1 micron.

The width of the nanowire can be, for example, about 5 nm to about 50nm, or more particularly, about 10 nm to about 30 nm.

In some embodiments, the length of the nanowire can be, for example,about 250 nm to about 5 microns, and have a width, for example, of about5 nm to about 50 nm. In other embodiments, the length of the nanowirecan be, for example, about 5 nm to about 50 nm, and have a width, forexample, of about 10 nm to about 30 nm.

When a plurality of nanowires is present, the lengths and widths can beexpressed as average lengths and widths using known statistical methodsin materials science. For example, the average length of the nanowirecan be, for example, about 250 nm to about 5 microns, or moreparticularly, about 400 nm to about 1 micron. The average width of thenanowire can be, for example, about 5 nm to about 50 nm, or moreparticularly, about 10 nm to about 30 nm.

Also, when a plurality of nanowires is present, the nanowires can besubstantially monodisperse in length and/or width. The monodispersitycan be accomplished, because the nanowires are assembled from scaffoldswith uniform length and width. Again, known statistical methods inmaterial science can be used to calculate the polydispersity for lengthand width. For example, images of the nanowires can be obtained and, forexample, 20-50 nanowires can be selected for statistical analysis. Thecoefficient of variation (CV) can be calculated wherein the standarddeviation is divided by the mean. The CV can be, for example, less thanabout 20%, more preferably, less than about 10%, more preferably, lessthan about 5%, and more preferably, less than about 3%.

The nanowires can be substantially straight. For example, straightnesscan be estimated by (1) measuring the true length of the nanowire, (2)measuring the actual end to end length, (3) calculate the ratio of truelength to actual end to end length. For a perfectly straight nanowire,this ratio will be one. In the invention, ratios close to one can beachieved including, for example, less than 1.5, less than 1.2, and lessthan 1.1.

The inorganic nanowires of the present invention can also be formed incombination with other types of conjugate materials to form largerstructures using, for example, multifunctional scaffolds. Hence, theconjugate material is not particularly limited to inorganic materialsfor these larger structures and combinations of materials can be used.In general, it will be selected for a particular application. It can beselected so that the virus particles can be subjected to biopanningagainst the conjugate material, and then the conjugate material isselectively or specifically bound to the virus particle. In someapplications, selective binding can be sufficient, whereas in otherapplications, a more powerful specific binding can be preferred.Examples of general types of conjugate materials which can be used inlarger structures include inorganic, organic, particulate,nanoparticulate, single crystalline, polycrystalline, amorphous,metallic, magnetic, semiconductor, polymeric, electronically conducting,optically active, conducting polymeric, light-emitting, and fluorescentmaterials. Conjugate materials are described further, for example, inthe patent publications and technical literature to Angela Belcher andco-workers cited throughout this specification.

In sum, the present invention relates to the general, universalsynthesis of 1-D nanostructures, including nanowires, based on, inpreferred embodiments, a genetically modified virus scaffold for thedirected growth and assembly of crystalline nanoparticles into 1-Darrays, followed by annealing of the virus-particle assemblies into highaspect ratio, crystalline nanowires through oriented, aggregation-basedcrystal growth (14, 15) (FIG. 2A). The synthesis of analogous nanowirestructures from fundamentally different materials, e.g., the II-VIsemiconductors ZnS and CdS and the L1₀ ferromagnetic alloys CoPt andFePt, demonstrates both the generality of the virus scaffold and theability to precisely control material characteristics through geneticmodification. In contrast to other synthetic methods (6), this approachallows for the genetic control of crystalline semiconducting, metallic,oxide, and magnetic materials with a universal scaffold template.

IV. Method of Making Inorganic Nanowires

The present invention also provides methods of making the inorganicnanowires, which are further exemplified in the below working examples.For example, the invention provides a method of forming an inorganicnanowire comprising the steps of: (1) providing one or more precursormaterials for the inorganic nanowire; (2) providing an elongated organicscaffold; (3) reacting the one or more precursor materials in thepresence of the scaffold to form nanoparticles, wherein thenanoparticles are disposed along the length of the elongated organicscaffold; and (4) thermally treating the scaffold and the nanoparticlesto form the inorganic nanowire by fusion of the nanoparticles. In someembodiments, the thermal treatment is not performed, and the methodcomprises the steps listed as (1)-(3) above. This method of forming ananowire can also be used to form a plurality of nanowires.

In these methods, the inorganic nanowires are described in the previoussection including the crystallinity, types of materials, size includinglength and width, monodispersity, and straightness. Also, in thesemethods, the elongated organic scaffold is described above including theviral system with its potential for selective recognition. These methodsinclude situations involving the substantial removal of the organicscaffold.

The invention is not particularly limited by the type of reaction andthe precursor materials used to form the nanowire. In general, thereaction and the precursor materials should be compatible with thescaffold. Reactions at temperatures of below 100° C. can be used to formthe nanoparticles. In a preferred embodiment, the treating stepcomprises a chemical reduction of metal precursor salts. Precursormaterial can be preformed nanoparticles or materials that formnanoparticles, for example.

In a preferred embodiment, the nanoparticles can have an averagediameter of about 2 nm to about 10 nm, and more particularly, about 3 nmto about 5 nm. The nanoparticles can be crystalline before and/or afterthe thermal treating. The nanoparticles can be fused before and/or afterthermal treatment. For example, the thermal treatment may act to fusethe nanoparticles, which were not fused prior to the thermal treatment.The nanoparticles can be oriented or not oriented.

The temperature and time of the thermal treatment step are notparticularly limited but can vary depending on the precursor materialsused and the material of the final nanowire. For example, the meltingtemperatures and annealing behavior of the materials can be consideredin selecting temperature. In general, temperatures of about 100° C. toabout 1,000° C. can be used. Thermal treatment can be used to fuse thenanoparticles into a single structure and also to remove the scaffold,tailored for a particular application with particular materials. Inprinciple, the porosity of the nanowire and the degree of fusion of thenanoparticles can be affected by the temperature. In a preferredembodiment, the thermal treatment step can be carried out at about 300°C. or higher, up to about 500° C. In general, and depending on thematerials, lower temperatures can be used such as, for example, about200° C. to about 300° C. if more porous nanowires are desired with lessfusion. The thermal treatment step can be carried out at a temperaturebelow the melting temperature of the precursor material. The temperaturecan be selected to achieve a desired crystalline phase which may be alow energy phase or a high energy phase. If desired, a temperatureprogramming step can be used to tailor the fusion of the nanoparticles,the targeted crystal phase, and the removal of the scaffold, if desired.Higher temperatures of, for example, about 500° C. to about 1,000° C.can be used to ensure the scaffold is completely removed and burned off.Lower temperatures, for example, about 50° C. to 300° C., can be used toavoid removing the scaffold. However, temperature and time can beselected so as to not result in excessive oxidation of the nanowires.The time of the thermal treatment is not particularly limited but canbe, for example, 30 minutes to 12 hours. Preferably, the temperature andtime for thermal treatment can be adjusted to achieve the optimumbalance for nanoparticle fusion while reducing oxide formation andimproving the stability of the crystal structure.

In one embodiment, the invention provides a process for producingnanowires with use of an elongated organic scaffold comprising the stepsof: (1) providing an elongated organic scaffold which comprises aplurality of binding sites including binding sites along the length ofthe scaffold and binding sites on at least one end of the scaffold; (2)disposing a nanowire precursor composition along the length of thescaffold to form a scaffolded precursor composition; and (3) treatingthe scaffolded precursor composition to form the nanowire. In oneembodiment, the elongated organic scaffold has binding sites at bothends of the scaffold. In another embodiment, the process furthercomprises the step of using the binding site at the end of the scaffoldto bind to another structure. The other structure can be, for example,another elongated organic scaffold. an electrode, a circuit element, asemiconductor material, an electrically conductive material, a magneticmaterial, or a biological molecule. The scaffold can be bound to apatterned structure, such as a circuit substrate. The treating step maybe a thermal treatment step as described in detail herein. The scaffoldcan be removed or left intact.

V. Applications

The nanowires of the present invention can be used in many differentcommercial applications, some of which are noted above, including thecited patent applications, and in the cited references at the end of thespecification. The nanowires can be used, for example, in applicationsrequiring electrical conductivity or semiconductivity at the nanoscale.The large surface area to volume ratio of nanowires is advantageous forapplications, such as, fule cells, thin film batteries, andsupercapacitors. In some applications, a single nanowire can be used. Inother applications, a plurality of nanowires can be used, whether in aparallel or crossed manner. In general, organized arrangements ofnanowires are advantageous. In some applications, the nanowire can besurface modified, doped, or otherwise modified in its material structurefor the application. Modifications include both chemical and biologicalmodifications. Microcircuitry, nanocircuitry, macroelectronics,photovoltaics, solar cells, chemical and biological sensors, opticalcomponents, field emitting tips and devices, nanocomputing,nanoswitches, molecular wire crossbars, batteries, fuel cells,catalysts, very large flat panel displays, tiny radio frequencyidentification devices, smart cards, phased array RF antennas,disposable computing and storage electronics, nanoscale bar codes, crossbar nanostructures, biosensor arrays, high density data storage, fieldeffect transistors, and the like are representative examples ofapplications for the nanowires. Particularly important semiconductiveelements include, for example, p-n diodes, p-i-n diodes, LEDs, andbipolar transistors. Nanowires can be incorporated into a number ofdevices, such as electronic, optoelectronic, electrochemical, andelectromechanical devices. A single nanowire can connect elements in adevice or a series of connected segments of nanowires can connectelements. For example, a field effect transistor device may comprisenanowires in both a parallel and crossed arrangement.

Applications of nanowires are described in, for example, U.S. patentapplication publication no. 2003/0089899 (published May 15, 2003) toLieber et al. and include, for example, field effect transistors,sensors, and logic gates, and this publication is hereby incorporated byreference in its entirety including its description of devices made fromnanowires. Additional applications of nanowires are described in, forexample, U.S. patent application publication no. 2003/0200521 (publishedOct. 23, 2003) to Lieber et al. and include nanoscale crosspoints, whichis incorporated by reference in its entirety. Additional applications ofnanowires are described in, for example, U.S. patent applicationpublication no. 2002/0130353 (published Sep. 19, 2002) to Lieber et al.and include devices with chemical patterning and bistable devices.Additional applications of nanowires are described in, for example, U.S.patent application publication no. 2002/0117659 (published Aug. 29,2002) to Lieber et al. and include nanosensors for chemical andbiological detection. In addition, applications for related nanorods aredescribed in, for example, U.S. Pat. Nos. 6,190,634; 6,159,742;6,036,774; 5,997,832; and 5,897,945 to Lieber et al. A number ofliterature references teach applications of nanowires and relatedtechnology, such as Choi et al., J. Power Sources 124:420 (2003); Cui etal., Science 293:1289-1292 (2001); De 1-leeret al., Science270:1179-1180 (1995); and Dominko et al., Advanced Materials14(21):1531-1534 (2002), which all of which are herein incorporated byreference in their entirety.

Of particular importance for this invention, the scaffold can be used todirect the nanowire to other structures so the scaffold is an activescaffold rather than a passive scaffold. For example, viruses can beconjugated with one-dimensional nanowires/nanotubes, two dimensionalnano electrodes, and microscale bulk devices. One-dimensional materials,such as nanotubes or nanowires, when conjugated with the pIII end of M13viruses, may form phase separated lamellar structures that haveinorganic nanotube or nanowire layers and phage building block layers.Two-dimensional nano-thick plate shaped electrodes can be organized.Viral-semiconductor composite nanowires can be attached across metalelectrodes, including noble metal electrodes such as gold electrodes,through binding sites at either end of the virus. The nanowire canbridge a source and a drain. The nanowire precursor can be disposed onor adjacent to the electrodes and then the scaffold can be removed sothat the nanowire can be intimately in electrical contact with theelectrode in a final state. The thermal annealing can be carried outprior to bridging the electrodes with the nanowire or after bridging thenanowire to the electrodes, as long as the nanowire ultimately functionsas a bridge. These structures can function as nano-FET devices withenhanced performance due to the c.a. 5 nm diameter of the gate region.Unlike other proposed nano-scale devices, where wire placement must bedone stochastically, this approach directs single wires to the correctelectrode locations. Alternative cathode and anode structures might beuseful for nanosize biofuel cells. When the specific binding M13 viruscombined with micro-size objects, periodic organization of thesemicro-dimensional objects is also possible. The role of the M13 viruswill be the specific adhesive unit to self-assemble multiple differentobjects in periodic patterns. The engineering ability of the M13'svarious proteins can be a key factor in the development of theseviral-inorganic hybrid-based arrays. In addition, fibers or fabric likenetworks of viruses can be constructed with specifically designedmechanical properties based on the secondary and tertiary structuresinduced by viral-viral binding. In addition these materials can havespecial properties impregnated into them by further functionalizing theviruses to bind regents or signaling elements.

Additionally, multifunctional viral based arrays can have uses in tissuerepair where one part of the array selectively binds to a tissue typewhere another part can nucleate bone or other structural bio-materials.Additionally, catalytic nano-structures can be developed by controllingelemental identity and geometrical arrangement of molecular catalyticmoieties.

The exploitation of the self-assembly motifs employed by the M13bacteriophage to produce a biological scaffold provides methods ofgenerating a complex, highly ordered, and economical template for thegeneral synthesis of single crystal nanowires. By introducingprogrammable genetic control over the composition, phase and assembly ofnanoparticles, a generic template for the universal synthesis of avariety of materials can be realized. Further advances in thefabrication of nanoscale materials and devices can be achieved throughmodification of the remaining four proteins in the virus to incorporatedevice-assembly directors. The ability of viruses to form liquid crystaland otherwise aligned and ordered systems, based on their shapeanisotropy, is another promising route for the assembly of virus-basednanowires into well ordered arrays on multiple length scales (11).Overall, modification of biological systems by the introduction ofsubstrate specific peptides presents a method of achieving well orderednanomaterials in a cost-effective and scalable manner.

In particular, when amino acid oligomers are expressed on a surface, theexpression of the amino acid oligomers may serve a number ofcommercially useful functions, including but not limited to, celladhesion factors, trophic factors, or binding sites for organic orinorganic molecules. Expression of amino acid oligomers allows theviruses to be engineered to specific applications. For example, thefilms or fibers comprising engineered fibers may contain amino acidoligomers that initiate or enhance cell growth for use in tissueengineering applications. In another example, amino acid oligomers withspecificity for a specific inorganic molecule may be expressed to bindthe inorganic molecule to increase the efficiency of a chemicalreaction. In still another example, the expressed amino acid oligomermay bind an organic molecule, such as a biodefense agent. Such films orfibers could be incorporated into the clothing of military personnel orfirst responders as part of a sensor system.

These are only a few examples of the utility of films and fibers madefrom engineered viruses, and other applications are readily apparent toone of skill in the art.

Working Examples

The present invention is further characterized by the followingnon-limiting working examples including FIGS. 2 and 3 and descriptionand discussion thereof. One skilled in the art can use as guidance FIGS.1-3 in the practice of the present invention which provide anintroduction to the working examples.

FIG. 1

FIG. 1A illustrates the nanowire synthesis scheme or the nucleation,ordering and annealing of virus-particle assemblies. FIG. 1B shows thesymmetry of the virus. The symmetry allows for ordering of the nucleatedparticles along the x, y, and z directions fulfilling requirements foraggregation based annealing. FIG. 1C shows the highly ordered nature ofthe M13 bacteriophage. The highly ordered nature of the self assembledM13 bacteriophage promotes the preferred orientation seen in nucleatedparticles through the rigidity and packing of the expressed peptides,which is visualized at 20% incorporation. FIG. 1D shows the construct ofthe M13 bacteriophage virus. The construct has genetically modifiablecapsid and ends, specifically the gPVIII, gPIII, and gPIX, which arecoded for in the phagemid DNA enclosed within the virus capsid.

FIG. 2

FIGS. 2A-F shows electron microscopy of both the pre- and post-annealedZnS and CdS viral nanowires. FIG. 2A shows Dark-fieldDiffraction-contrast imaging of the pre-annealed ZnS system using the(100) reflection reveals the crystallographic ordering of the nucleatednanocrystals, where contrast stems from satisfying the (100) Braggdiffraction condition. The inset of FIG. 2A shows the ED pattern of thepolycrystalline pre-annealed wire showing the wurtzite crystal structureand the single crystal type [001] zone axis pattern, suggesting a strong[001] zone axis preferred orientation of the nanocrystals on the viraltemplate. The electron diffraction (ED) pattern (inset of FIG. 2A) showssingle crystal-type behavior, even though the sample area is composed ofmany nanocrystals. This behavior suggests that the nanocrystals on thevirus were preferentially oriented with their c-axes perpendicular tothe viral surface. FIG. 2B is a Bright-field TEM image of an individualZnS single crystal nanowire formed after annealing. The upper left insetof FIG. 2B shows the ED pattern along the [001] zone axis shows a singlecrystal wurtzite structure of the annealed ZnS nanowire. The lower rightinset of FIG. 2B is a low magnification TEM image showing themonodisperse, isolated single crystal nanowires. FIG. 2C shows a typicalHRTEM of a ZnS single crystal nanowire showing a lattice image thatcontinually extends the length of the wire, confirming the singlecrystal nature of the annealed nanowire. The measured lattice spacing of0.33 nm corresponds to the (010) planes in wurtzite ZnS crystals. A 30°orientation of (010) lattice planes with respect to the nanowire axis isconsistent with the (100) growth direction determined by ED. FIG. 2DHAADF-STEM image of single crystal ZnS nanowires, which were annealed ona silicon wafer. FIG. 2E shows HAADF STEM images of CdS single crystalnanowires. FIG. 2F is an HRTEM lattice image of an individual CdSnanowire. The experimental lattice fringe spacing, 0.24 nm, isconsistent with the unique 0.24519 nm separation between two (102)planes in bulk wurtzite CdS crystals.

FIG. 3

FIG. 3A shows CoPt wires as synthesized by the modified virus templatewhere soluble in water. Reduction of Co and Pt salts without thepresence of the virus yielded large precipitates which immediately fellout of solution. FIG. 3B shows a TEM image of the unannealed CoPtsystem. The inset of FIG. 3B shows a STEM image of unannealed CoPtwires. The scale bar shown is 100 nm. FIG. 3C shows a low resolution TEMimage of crystalline L1₀ CoPt wires (about 650 nm×about 20 nm). Thetendency of the CoPt and FePt wires to not be straight may stem frommagnetic interactions between wires and/or nanoparticles not present inthe II-VI systems. The inset of FIG. 3C is an ED showing thecharacteristic (110) and (001), L10 lines, and the crystallinity of thesystem. FIG. 3D is an HRTEM of the CoPt wires with the (111) planeperpendicular to the c-axis of the wire. The inset ED reveals thesuperlattice structure unique to the L10 phase. FIG. 3E is a TEM imagingof the unannealed FePt wires. FIG. 3F shows a TEM of the annealed FePtwires. The inset ED pattern confirms the L10 nature of the FePt wiresand shows the crystalline nature of the material.

Engineering M13 Bacteriophage

The M13 bacteriophage used in the working examples is a high productionrate virus (200 mg/L) comprised of five genetically modifiable proteins(19, 20, 21); gene products (gP)-3, 6, 7, 8 and 9, of which ˜2700 copiesof the gP8 protein forms the capsid of the wild type virus. The gP8protein was genetically modified and expressed using a phagemid system,resulting in fusion of the substrate specific peptides to the N-terminusof the gP8 protein (12). During assembly, stacking of the gP8 unit cellresults in a five-fold symmetry down the length (c-axis) of the virusand is the origin of the ordering of fusion peptides in athree-dimensional structure (FIG. 1B). Computational analysis of peptideexpression on the capsid of the virus revealed that the nearest neighborpeptide separation stabilized around 3 nm at and above 20% incorporation(FIG. 1C). Consequently, high incorporation of the substrate specificfusion peptides is not required for complete mineralization of the virusto occur. Tri-functional templates can be realized through furthergenetic modification of the proximal and remote tips of the virus(specifically the gP3 and gP9 proteins, 22) which can be used to pushthe current system to higher aspect ratios and introduce materialsincluding materials such as, for example, noble metals, semiconductors,and oxides to assemble functional heterostructured materials (FIG. 1D).

Mineralization of Scaffolds

Mineralization of the ZnS and CdS systems have been described previously(11, 12; 17) and involves incubation of the viral template with metalsalt precursors at reduced temperatures to promote uniform orientationof the nanocrystals during nucleation (23), leading to the preferredcrystallographic orientation of nucleated nanocrystals with respect tothe long axis of the virus. Prior to annealing, wurtzite ZnS and CdSnanocrystals (3-5 nm) grown on the virus surface were in close contactand preferentially oriented with the [001] direction and the (100) planeperpendicular to the wire length direction, which is supported byElectron Diffraction (ED), High Resolution Transmission ElectronMicroscopy (HRTEM), High Angle Annular Dark Field Scanning TransmissionElectron Microscopy (HAADF-STEM), and Dark-field Diffraction-contrastImaging (FIG. 2) (24). Particles attached to the virus were likelyprohibited from fusing under initial synthesis conditions likely due forexample to the blocking effects of the neighboring peptides, andtherefore removal of the template was desired in order to form singlecrystal nanowires. Thermal analysis of the virus-particle system showedcomplete removal of the organic materials by 350° C. (25), whichcorresponded to the minimum temperature observed for the fusion ofadjacent particles by TEM with annealing performed in situ using athermal stage (26).

Formation of Nanowires

Annealing of the mineralized viruses at temperatures below the ZnS andCdS particle melting point (400-500° C.) allowed the polycrystallineassemblies to form single crystal nanowires (for ZnS nanowires, lengthdistribution was about 600-650 nm; for CdS nanowires, lengthdistribution was about 475-500 nm; the diameters for ZnS and CdSnanowires were about 20 nm) through removal of the organic template andminimization of the interfacial energy (27) (FIG. 2B, E). ED and HRTEMrevealed the single crystal nature of individual nanowires thatinherited the preferred orientation seen in the precursorpolycrystalline wires through removal of the grain boundaries (28, 29)(FIGS. 2C and D). The [100] direction and (001) plane orientations ofthe observed ZnS nanowires where consistent with common elongationdirections for II-VI nanowires, even though these are thermodynamicallyhigh energy planes (FIGS. 2B and C; 14, 30, 31). HRTEM of the singlecrystal CdS nanowires revealed a lattice spacing of 2.4 Å that wasconsistent with the unique 2.4519 Å separation between two (102) planesin bulk wurtzite CdS crystals (JCPDS #41-1049). The 43.1° orientation of(102) lattice planes with respect to the nanowire axis indicated thatthe nanowire was elongated along the [001] direction and again confirmedthe wurtzite structure (FIG. 2F).

Formation of Ferromagnetic Nanowires

Extending the virus-directed synthesis approach to the ferromagnetic L1₀CoPt and FePt systems was carried out for demonstrating both thediversity of applicable materials and to address current technologicalissues regarding the development of low-dimensional magnetic materials.Platinum alloyed magnetic materials of the chemically ordered L1₀ phasehave been of recent interest due to their high coercivity, resistance tooxidation, and inherent magnetic anisotropy important for ultrahighdensity recording media (32). Although synthetic routes such as VLSyield exquisite 1-D semiconducting structures and non-specific templateschemes are applicable to a range of materials, both have faceddifficulties in producing high-quality, crystalline metallic andmagnetic nanowires in free standing form (33).

Genetically Engineered Scaffolds

The M13 bacteriophage was modified by fusing either the CP7 CoPtspecific or FP12 FePt specific peptide into the virus capsid. Nucleationof the CoPt and FePt particles was achieved via the chemical reductionof metal precursor salts in the presence of gP8 modified viruses (18,34). Annealing of the assemblies at 350° C. promoted the growth ofcrystalline CoPt and FePt nanowires of the L1₀ phase that were uniformin diameter (10 nm+/−5%). The crystalline nature of the wires can beseen in the selected area ED pattern, which also shows thecharacteristic (001) and (110) L1₀ peaks, and by high resolution TEMlattice imaging (FIG. 3C, D). The (111) plane perpendicular to the longaxis of the CoPt wires with a lattice spacing of 2.177 Å was inagreement with the reported value of 2.176 Å, and again confirmed thehighly crystalline nature of the material (FIG. 3D, JCPDS #43-1358). Thepersistence of the L1₀ phase, which is kinetically accessible above 550°C. (15), was attributed to the propensity of particles to maintain theirorientation during aggregation-based annealing.

Nanowire Design Simulations

The invention including the working examples can be further understoodwith use of simulation methods. For example, Monte Carlo simulations ofthe A7 constrained sequence resulted in a 21% decrease in the standarddeviation of backbone dihedral angles upon transfer of the peptide fromisolation into the capsid environment, demonstrating the rigidityimposed on the fusion peptide (35). Ordering of the nucleated particleswith regards to preferred crystallographic orientation along the lengthof the virus was believed to be a result of the stability of the peptidefusion and the symmetry of the virus coat. This nanocrystal orderingpromoted the single crystal nature of the annealed nanowires bysatisfying the orientation requirements of the aggregation-based crystalgrowth mechanism (14). Although particles exhibiting orientations notcoherent with that of the majority were to be expected, these minoritynanocrystals should rotate to adopt the preferred crystallographicorientation and merge with the majority to minimize both the interfacialand grain boundary energies (31, 36, 37). Additional experimentaldetails can be found in several of the below footnotes.

Although making and using various embodiments of the present inventionare discussed in herein, it will be appreciated that the presentinvention provides many applicable inventive concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed herein are merely illustrative of specific ways tomake and use the invention, and do not delimit the scope of theinvention.

The following references are not admitted prior art but can be used toguide one skilled in the art in the practice of the present invention,and also are incorporated herein by reference in their entirety.

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1. A method of forming a nanowire, the method comprising: (i) providingan inorganic nanoparticle precursor; (ii) forming a plurality ofnanoparticles from the precursors on a surface of a virus, and (iii)thermally treating the nanoparticles on the virus to form the nanowire,wherein the nanoparticles comprise a metal, a metal oxide, or acombination thereof.
 2. The method of claim 1 further comprising forminga scaffold of viruses by providing viruses that bind to a desiredsubstrate or to each other prior to thermal treatment.
 3. The method ofclaim 1, wherein the nanowire is substantially free of a virus.
 4. Themethod of claim 1 further comprising fusing the plurality ofnanoparticles to form at least one nanowire.